ST. LOUIS -- Shelby Miller's brief transfer to the bullpen has concluded, as the Cardinals announced on Wednesday that Miller will return to the rotation on Saturday to face the Cubs. Concurrent with Miller's transition back to starting, Carlos Martinez will shift to the bullpen, where he is immediately ready for use.

The Cardinals opened the second half with Miller in the 'pen as part of the organization's plan to weave a period of rest into the regular season for the second-year starter. Miller last started on July 10, when he walked four and allowed four runs in a five-inning loss to Pittsburgh. His only appearance since then came out of the bullpen in Sunday's one-inning appearance.

"I think we accomplished what the goal was from the beginning of 'let's get him some rest,'" manager Mike Matheny said. "He's had a nice little period here to get himself right and strong and feeling good. Now we have to get him out on the mound and watch him get the consistency."

The Cardinals are looking for the same consistency from Martinez, though the 22-year-old right-hander will now try to find it while pitching in relief. He made seven starts after joining the rotation in mid-June, but didn't pitch into the fifth in either of his most recent two. He finished six innings only once.

"He hit it right on the mark -- consistency with his stuff and consistency in the strike zone and continue to get better with his offspeed stuff," Matheny said of Martinez's spoken checklist of areas for improvement. "It's frustrating, I'm sure, for a kid who has that kind of stuff not to be able to replicate it from inning to inning. It just comes down to execution. He's going to get there."

The Cardinals are not committing to whether Martinez will rejoin the rotation next month once the Cardinals again need a regular fifth starter. Martinez will remain an option, as will current members of the Triple-A Memphis rotation. There is also the possibility that the Cardinals add a starter via the trade market before the July 31 non-waiver Trade Deadline to fill that spot externally.

"Once we get to that stage, get that decision, we'll see who fits it best," Matheny said. "It could be him, and it might not. That's the message he has right now. He just needs to go pitch and take whatever role he can fit in right now to go get better."